Method of washing glass surfaces



Patented Aug. 19, 1947 METHOD OF WASHING GLASS SURFACES AND COMPOSITION Walter F. Wegst and Leslie R. Bacon, Wyandotte, Thomas H. Vaughn, can J. Crawford, Wy

Grosse lie, and Dunandotte, Mich., assignors to Wyandotte Chemicals Corporation, Wyandotte, Mich., a corporation of Michigan No Drawing. Application February 10, 1944, Serial No. 522,190

The present invention relates to a method and product for preventing the glass-dissolving action of alkali solutions. Our invention is particularly applicable to alkali detergent compositions used in the washing of glass containers or those having glass or vitreous ceramic exposed surfaces.

We have made the unexpected discovery that compounds of the elements of group II-A, IV-B and V-B of the periodic table, below and including Serial 6 thereof, when added to the alkali solution in relatively small amounts are effective in protecting glass and ceramic surfaces against attack and deterioration. These include more or less alkali-soluble compounds of the elements tin, barium, strontium, bismuth and antimony. Compounds of the element lead in group IV-B are found to be not as good as tin compounds in the same group and subgroup. The valence of the element is not a controlling factor, since both the stannous and stannic forms of tin compounds were inhibitors against scuffing. The compounds of these aforesaid elements do not include those of the radio active elements falling within these groups. Although other alkali hydroxides than sodium hydroxide such as potassium hydroxide can be used, only the former is commercially practicable. These compounds so far as we know do'not impair the detergent or germicidal activity of the alkaline washing solution.

While our invention is herein described with particular reference to the cleansing of glass bottles. such as milk and beverage bottles, such invention is similarly available in general in the cleansing by alkaline detergents of glazed or vitreous ceramic surfaces, such as those of mixing kettles, holding vessels, pasteurizers, etc., widely used in the food industries, where the emcient germicidal and strong cleansing action of alkali would be desirable but for its corrosive action.

It is the common practice in the bottling of dairy products and a variety of beverages to refill and reuse the glass bottles many times over, during their normal life. When such bottles are returned to the bottler after being emptied by the consumer, it is highly important that they be subjected to a vigorous and thorough washing, not only to remove residues, dirt and soil and similar contamination and thus to render them physically clean, but also to subject them to a germicidal 2 Claims. (Cl. 252-456) action in order to render them sterile and free from bacterial or fungal contamination. Washing solutions of relatively high alkaline strength have been found most suitable in practice for a washing operation of this nature. Caustic alkali, e. g. sodium hydroxide, is the major ingredient of most such alkali washing solutions. In fact, several State laws require a minimum NaOH content in the bottle washing solutions employed by bottling plant operators.

Other ingredients commonly employed in limited proportions in addition to caustic soda are the carbonates, orthophosphates and silicates of soda. To a more limited extent commercially, pyrophosphate, polyphosphates and borates of soda, and surface active agents, may be similarly employed. Small proportions of neutral salts, of which sodium chloride or sodium sulfate are representative examples, are not uncommonly introduced, either accidentally as impurities or to attain desired objectives. Any impurities of the water supply will, of course, be present, either in original form or as modified by reaction with constituents of the alkaline solutions, and further in some cases, reagents added separately for softening or special conditioning of the water supply.

It has been found, however, that such alkali washing solutions, e. g., a solution having 1 to 10% by weight NaOH content, have a serious and objectionable glass-dissolving action which is particularly emphasized under conditions of commercial bottle washing operations where the alkali solution is heated and the glass bottles handled in a mechanical washing machine. This glass-dissolving action abets mechanical action, 1. e. physical contact and abrasion of the bottles in the washing machine, and results in a deterioration of the surface appearance of the glass, producing scufied, etched or worn effects thereon; dulls the brightness and original clear, brilliant appearance of the glass; deteriorates glass frit color labels fused onto the surface of the bottles; and results in a weakening of the strength of glass bottles, rendering them more liable to breakage and explosion after filling and crowning, particularly in the case of pressure retaining vessels, such as carbonated beverage bottles.

When glass bottles or beverage containers are returned to the bottling plant for washing prior to refilling, they are ordinarily passed through 3 either soaker type or hydraulic typewashing machines. In 'a large machine of the soaker type, a typical cycle of operations would consist in the following:

In practice the number and sequence of cleansing steps is subject to considerable variation, however, and this is true also of temperatures and concentrations of solutions employed. The step 20 of chlorination is most commonly employed in the washing of dairy bottles.

The practicable ranges of temperature and concentration for the alkaline solution are usually taken to be 120-165 F. and 1 15% caustic respectively, as hereinafter defined; although as high as 10% caustic may be employed under certain rigorous washing and cleaning conditions. The efiects o1 soaking time, alkaline concentration and temperature are interrelated in the so sense that increased temperatures and/or concentrations diminish the soaking period required to attain a given standard of cleansing and germicidal'performance. It is'known further that increases in temperature 01' the alkaline are reflected in increased deterioration of the glass surfaces, and it is generally true that within the practicable economic limits increased concentrations are reflected in increased corrosion and dissolution of the glass. The period of exposure 40 or bottles to the detergent solutions will usually run upward of 5 minutes per complete'cleansing cycle in soaker type machines.

Hydraulic type machines operate on the principle of projecting streams or and rinse waters at high velocity upon the bottles internally and externally rather than passage of bottles through soaker tanks. Due to the vigorous mechanical action, the practicable concentrations of and exposures to strongly alkaline solutions may run somewhat lower than for soaker type machines.

In either type machines, the alkali content of the washing solution is maintained by suitable tration is the determination of actual caustic soda content, the ordinary practicable ranges of which may be taken to be 15%, dependent on other conditions hereinbefore'reierred to.

It has been determined that the alkali attack upon glass bottles during such a washing treatment is in the nature of a dissolution of the glass by the alkali; hence, a determination or the weight loss of glass bottles subjected to the action of an alkali washing solution presents a reliable criterion for measuring the degree of such attack.

We have determined that when a caustic soda solution is so tested, that the loss in weight, the glass-dissolving action, progressively increases with concentration and time of exposure.

The following examples will further illustrate the nature of this invention, but the invention is not restricted to these examples.

EXAMPLE I The glass bottles subjected to this test were glass beverage bottles of approximately 6 fluid ounces capacity and weighing approximately 393:3 grams. The bottles were filled with the 5 water-caustic alkali solution under test, sealed solutions 5 additions (make-up) from time to time. Control 55 in the field may be exercised through indicating All percenta e proportion values given throu hout h rein are by wefight. g

and held six days at 185 F. The solutions were in each cas clear upon initial preparation.

The following table represents the results on the eifect of tin compound:

Table I Loss of Weight (in Total Solids in Soln.

milligrams) At Per (by weight) Cent Concentration N on "t i 1'7 39' 5'7 NaiSnO;.3H 0

100 o 149 1,180 1,471 95 5 682 616 766 90 10 501 m 911 so 20 295 532 641 alkaline solution b Acid rinse applied to remove scale deposits not removed by hand rushing alter kali exposure.

Exmru II case to ml. of water and to each of these, 100

ml. 01' 6% sodium hydroxide were added. Thus 200 ml. of test solutions, approximately 3% in NaOH strength were prepared. The same conditions as to time and temperature were employed as in Example I supra.

The following are findings on compounds of elements in groups lI-A, IV-B and V-B of the periodic table:

Table II Periodic Classification Wei hi; 0! in Initial Inhibitor Inhfimm We 1: cl Condition (in M) Bott es (in of Group series milligrams) Solution Strontium Chloride (SrCl iiHgO) II-A 6 0. 564 171 Ppt. Strontium Sulfide (Br II-A 6 0.246 92 P t. Barium Chloride (BaCl, 2H 0).. 11-}. 8 0.276 177 o p Bismuth Trlchloride (BiC V-B 11 0. 274 975 No ppt. Antimony Trlchloride (BbCh).-- V-B 7 0. 340 896 N0 ppt. Stannpus Chloride (SnCl .2H,0) IV-B 7 0. 346 818 No ppt. Stanmc Chloride (SnCh) IV-B 7 0. 398 722 No ppt.

meters or by simplified chemical test methods. One common basis for controlling alkali concen- From the foregoing Table 11, it will be seen that the amount of S1C12.6H20 calculates to be 5.7% by weight on the anhydrous basis of the NaOH present in the solution, viz:

255.6 By similar calculation, each of the other inhibitor compounds in Table H, on the anhydrous basis, are found to be present in the following percentage amounts of the NaOH present:

In the formulation of commercial detergent compositions, according to the teachings of our invention other alkaline detergent materials may, of course, be present. Such alkaline detergent materials are the alkali metal phosphates, -carbonates, -borates and -silicates, such as trisodium ph phate, sodium tetraphosphate, sodium carbonate, .b'orax and sodium metasilicate. These alkaline ingredients may be present in amounts less than, equal to or greater than the weight of the inhibitors mentioned supra. The criterion of our invention is that, regardless of the particular alkaline compound present other than caustic soda, the actual NaOH content of the resultant washing solution shall be 1-10% and the content of the inhibiting element in the additive less than the weight percent of the NaOH.

It is apparent that many widely different embodiments of this invention may be made without departing from the spirit and scope thereof and, therefore, we do not intend to be limited except as indicated in the appended claims,

being present in the amount weight, on the anhydrous basis, of the NaOH.

We claim:

1. A washing solution deterring the corrosive attack of caustic alkali on glass and ceramic surfaces consisting of approximately a 3% by weight aqueous solution of NaOH and a water-soluble chloride of a metal selected from the group consisting of Sr, Ba, Sn, Sb and Bi, said chloride of 3.96.6% by 2. A method of washing glass objects and objects with ceramic surfaces comprising the step of contacting the object with a heated aqueous solution of approximately 3% by weight NaOH content, and inhibiting the corrosive attack of the NaOH on such objects by incorporation in such solution 3.9-6.6% by weight of the NaOH present, on the anhydrous basis, of a water-soluble chloride of a metal selected from the group consisting of Sr, Ba, Sn, Sb and Bi.

WALTER F. WEGST. LESLlE R. BACON. THOMAS H. VAUGHN. DUNCAN J. CRAWFORD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,241,984 Cooper May 13, 1941 2,303,397 Schwartz Dec. 1, 1942 2,303,399 Schwartz Dec. 1, 1942 2,380,284 Young July 10, 1945 OTHER REFERENCES Chemical FormularyBennett; vol. 4, (1939), page 507. 

